Spray Polyurethane Foam On The Underside Of Your Roof Sheathing

Should i put any membrane or the like on the underside of the roof sheathing before spraying the foam in.

Spray polyurethane foam on the underside of your roof sheathing.

Some houses with open cell spray foam installed on the underside of the osb roof sheathing have had moisture problems. No airsealing hence i want to remove the fiberbatts and spray 3 inches of closed cell spray foam in before putting the fiberbatts back in place. Polyurethane or polystyrene spray foams can provide thorough coverage to roof rafters and attic walls in much less time than is needed for other materials. If you are installing spray polyurethane foam spf up against the underside of the floor in the crawlspace then your termite inspector can continue to inspect for termites around the perimeter.

The osb got wet and rotted. This construction approach was first used in the 1970s and it has been implemented much more widely since it was first included in the international code council s icc model building code in 2007 irc section 806 4. I have a conditioned attic currently insulated with r19 fiberbatts between the rafters. A layer of spray polyurethane foam can be installed against the underside of the roof sheathing with the rest of the rafter cavity filled with air permeable insulation.

Unlike solid insulation products that require careful measurement cutting and fitting spray foam can cover even the most uneven surface instantly. But where does the moisture come from. You must meet the same minimum code requirements for the spray foam layer and the total assembly as for the rigid foam plus air permeable insulation approach. The attic is unvented for instance no ridge vent exists.

If you are installing spf on the walls of the crawlspace then you need to leave an inspection strip around 6 wide on the walls. The roofing materials are installed and consist of timberline shingles and full coverage ice and water barrier the entire roof. The authors of the first paper cited a study in south carolina where the relative humidity in the attic was way too high in summer 80 to. Most unvented attics incorporate spray polyurethane foam spf on the underside of the roof deck and attic walls.

There have been isolated moisture related incidents that raise potential concerns about the overall hygrothermal performance of these systems.